The days of grabbing a three dollar bag of “thinset” and sticking floor tile right to the plywood in a bathroom are long gone (for professionals, anyway). For a proper tile installation you need a proper substrate. One of the most readily available are cement backerboards. These include products such as Hardiebacker, Durock, Fiberboard, wonderboard and a host of others.
When properly installed on your floor it is an ideal tile substrate for a quality and lasting installation. Notice I said typed “properly installed”? Laying them down on the floor and shooting drywall screws through them does not constitute proper installation.
Choose your weapon. I prefer Hardiebacker or Fiberboard. Whichever you choose make sure you get the proper thickness. With rare exception the 1/2″ variety would be the best choice simply because I like to overbuild stuff. With proper floor framing and deflection ratios, though, you can use 1/4″ to minimize height differences. This is not to say that 1/2″ adds significant sturdiness to your floor – it does not.
Dry fitting Backerboard on floor
You need to realize that cement backerboards, or just about any tile flooring substrate, does not add deflection stability to your floor. That is the up and down movement in your floor when you walk, jump, or use a pogo stick on your floor. The backerboards will not significantly diminish that movement. This needs to be addressed by adjusting your floor joists and framing – not by adding stuff on top of them. If your floor is bouncy without the backerboards it will still be bouncy with them.
Bouncy is not good for tile. (There’s a sentence I never thought I would say type.) I will, however, address deflection ratio in another post.
Start by ‘dry fitting’ all your pieces. This simply means cut and lay your pieces into the room without attaching them. Get all your pieces cut, holes cut out, and doorways undercut to fit and lay everything in there just like it will be when installed. This saves a load of time, mess, and headaches.
Backerboards dry fitted - notice gaps in seams
The joints in backerboards should be staggered. that just means that none of the seams should line up across the room and no four corners should be placed together. By staggering the seams you add strength to the installation simply by not having a significant weak point in the substrate.
You also want to leave 1/16 to 1/8 inch gap between each sheet – do not butt them together, and around the perimeter. If you butt them together you leave no room for expansion. The backerboard will not expand, but your walls will. If everything is butted tight and your wall expands into the room guess what happens. That’s right, your dog may burst into flames and no one wants that! It will also cause your floor to pop loose and possibly ‘tent’ or peak at the seams.
Beneath the backerboards you need thinset. Just about any thinset will work but you need to have it there. skipping this step virtually eliminates the purpose of preparing your substrate for tile – you may as well go grab that three dollar bag and start setting tile now. You need it – really.
Installing thinset beneath backerboards
Now that you have them all laid in there properly pick one side of the room to start on and pull a row out. You should only pull out one row at a time to place thinset beneath. That way you can replace them easier and in the proper position. If you pull out the entire room you may get to the last piece and discover everything has shifted 1/2″ and the last piece needs to be cut again. Not really a big deal but you won’t realize it until the backside of it is covered with thinset and you now need to pull it up, wipe the thinset off the wall from pulling it up, cut it, clean the thinset off your saw, snuff out the flames engulfing your dog (again), and replace it. It’s a bit easier just to pull one row at a time.
You need to trowel thinset onto your floor. I cannot overemphasize this (well, I could but you’d get sick of hearing it). This step is imperative for a proper tile installation. The thinset is not meant to ‘stick down’, adhere, or otherwise attach your backerboard to your subfloor. It is simply put in place to eliminate voids beneath your backerboard. Once laid into the thinset bed the floor becomes a solid, fully supported substrate for your tile – that’s what you want.
If you have an air pocket or some certain spot in your floor that is not level or flat with the surrounding area and you simply screw your backerboard onto it this will create a weak spot in your floor. Constantly stepping on that spot will, over time, loosen the screw and your floor will move.
When your floor moves your grout cracks. When your grout cracks your tile may become loose. When your tile becomes loose your tile may crack. When your tile cracks your dog will burst into flames – again. Put thinset beneath your backerboard. And put your dog out.
Installing thinset beneath backerboards
Once you have the area fully covered with thinset you can lay your backerboards into the bed of thinset and screw it down. DO NOT use drywall screws! Let me repeat that – THAT! Drywall screws are not made, nor are they sturdy enough for your flooring. You will either bust the heads of the screws off or be unable to countersink them into the backerboard. Hard to get a tile to lay flat over the head of a screw.
There are screws made specifically for cement backerboards. You should be able to find them at any hardware or big box store. They have grooves on the underside of the head which will dig into the backerboard and create its own ‘hole’ in which to countersink the head as it is screwed in. How cool is that? If you look closely at the photo you can see the ‘grooves’ beneath the head. They are more expensive than drywall screws – just so you know. But you need to use them.
Each manufacturer has their own specific spacing instructions for screwing down the backerboards – follow them – really. Some say every 12″ and some want every 6 – 8 inches. The board you use will determine the spacing. (And its right there on the sticker so don’t tell me you couldn’t find it.)
Start your screws in the center of the board and work out. This eliminates undue stresses on the boards. If you screw all the way around the outside and it is not perfectly flat you are going to have to release that pressure somewhere and it
Backerboard screw
won’t happen until you have all that pretty tile on top of it. Working from the center out eliminates that. It would probably never, ever be a problem but if you’re anything like me your installation would be the millionth one for that one in a million occurrence.
Backerboard placed into thinset and screwed down
Your floor is probably too thick (should be) for the backer screw to actually penetrate into the floor joist. If not, or just to be safe, do not place screws into the area above the floor joists. The plywood or chipboard which makes up your floor will expand and contract at a different rate and, more than likely, in different directions than your joists. If you screw your backer into the ply and into the joist six inches over it will cause inconsistent movement – no good. Do not screw your backerboard into your joists.
After I have all my floor down I will go back and double the screws around every seam. Just put another screw between every screw along the seams. It helps me sleep better at night.
The last thing you need to do is tape your seams. Get an ‘alkali resistant’ mesh tape – similar to drywall tape – and place it over all your seams in your floor. Then mix up some thinset and trowel it over the tape with the flat side of your trowel. Just like taping and mudding drywall. This will make your floor one large monolithic structure and lock it all together. You want alkali resistant tape so it will not break down due to chemicals present in most thinsets. I do not have photos of this because I do it as I set tile.
That’s it! Congratulations, you now have a perfect floor for your perfect tile installation. When installing floor tile – or any tile for that matter – the most important aspect of the installation is always the preparation. Everything beneath your tile is important, if any one aspect is done incorrectly it may compromise the integrity of your installation. Take your time and do it correctly, you will be much happier for it.
Now go put your dog out.
Good article…poor dog.
Is it ok to use a self leveling product on the subfloor, then screw through the dried leveling product when attaching the tile backer? I wasn’t sure if either the leveling product would crack while trying to drive a screw through it, or if the screws could even penetrate the concrete like material.
I’m looking at an unlevel subfloor and wondering what’s the correct course of action.
Thanks.
Hi Chris,
If you use SLC the tile is bonded directly to it after it cures, or you can use a membrane like ditra which is installed with thinset. Do not attempt to nail or screw through the slc. You don’t need backer when you use it.
My bathroom floor has a definite creek in it when walking on it. I cannot find how to reinforce the floor joist from below in our basement. Every floor joist in the basement below the bathroom appears to be structurally sound. Will putting thinnest with 1/4 inch backer board down possibly take care of this creaking noise. Or do you think this is not a good bathroom to tile?
Hi Kerry,
No it won’t, but driving screws into the joist to fasten the plywood to them solidly will. Most floor creaks are the plywood subfloor rubbing against the screw or nail that it is fastened to the joists with. When that movement either wears a wider hole in the plywood or the fastener loosens it will cause that creaking. Go down each joist with screws about every six inches and it should take care of it.
I have to ad 12″ of tile to my existing wood stove hearth to bring it up to code. I don’t know if the previous owner of the house installed backerboard under the tile or not. Apparently the tile is well done as it’s been there since at least 2007 that I know of and there don’t appear to be any cracks or problems.
My questions are.
1) Do we have to rip up everything to do this properly or can we get away with just adding 12 inch tile in the required layout?
2) Can we ad backerboard (or whatever it’s called, sorry I’m a girl lol ) under our ad-on tile and it will still work out even if there isn’t any under the previous install?
Thank you so much for your help.
Hi Charmaine,
You can just add 12 inches of tile to the existing. Unless the code specifically calls for backerboard behind the tile you can also just bond it directly to the drywall. it will be fine no matter what substrate is beneath the existing tile.
Roger, one more question: I used hardiebacker boards, and bought Rock-on screws (as I read later, “for use on durock or wonderboard”). Maybe because the screws were not specifically made for hardiebacker, they didn’t sink all the way through, but their heads are slightly (1/32-1/16) above the board.
I tried to take the screw out, enlarge the hole and screw it back, but it is a lot of work to do with all my 720 screws…
Do heads of the screws have to be completely countersunk? Or the thinset will cover them anyway? Should I use trowel with bigger squares (3/8 or even 1/2 instead of 1/4, as I planned to do)?
Hey Alexander,
If you use a 3/8″ trowel all your problems will be solved. (well, with the screw heads, anyway…) They don’t have to be countersunk, it just makes it much easier.
Roger,
Great site. I am replacing some solid hardwood floor (1/2″)with tile for certain parts of the room. There is 3/4″ T&G plywood beneath and cement foundation under that. Since the new tile will join up to the hardwood floor in some spots, I don’t want to have a height difference of too much. My concern is putting the backerboard over the 3/4″ plywood. If I use 1/4″ backerboard, the backerboard screw (1 1/4″) will end up hitting the foundation. Using 1/2″ backerboard will raise the floor up too high when I add the tile (~.374″) along with the thinset layers. Ideas? Since this is high traffic area, I want to do it right by putting the backerboard down with thinset and screws. Do they make 1″ backerboard screws? Thank you.
Hi Tom,
No, they don’t make 1″ backer screws. You can put it down with galvanized roofing nails, you can get those in 1″.
Learning a lot with your answers….
Can I install this backer board on top of an uneven plywood subflor? (due to a water damage?
Thanks a lot!
Hi Marina,
You can, but I would be concerned with the stability of the plywood. If there was water damage then it likely separated the layers of the plywood, so it’s probably not strong or stable enough for tile without being replaced.
Sorry, I know you didn’t want to hear that.
Roger,
Is there any objection on your part to using a pre-mixed thin set mortar under backerboard? The mortar will go on top of 1″x6″ T&G boards laid diagonally and below the 1/4″ BC plywood backerboard. I am using a crack/sound suppression membrane on top of the 1/4″ ply.
Scott
Hi Scott,
Yes, lots of objections. Pre-mixed ‘thinset’ is not thinset – it’s mastic with sand in it. It requires air to cure, which it will not get for a LOOOOOONG time under backerboard. Use the powdered thinset you mix with water.
Your website is fantastic! I was so afraid to try my hand and tiling but with your advice I feel confident enough to go for it. Thank you!
Here’s my question… I didn’t to put thinset under my cement board :-( It is screwed right into the substrate. Can I simply unscrew it, put down the thinset, then reuse the same cement board or will I need to replace it? Should I get new screws, use the same screw holes?
Hi Wendy,
You can just unscrew it and install your thinset, then rescrew it.
Roger,
Great website! Lots of good information explained very well. Much appreciated. I am installing a tile floor over some old linoleum in a bathroom and framing out some shelves and casing to hide the plumbing on the short sides of the new tub and ultimately tiling the wall along the wall.
1) Should I remove linoleum to expose T&G or can I just put plywood then thinset then backerboard directly over old linoleum?
2) Should I put some type of vapor barrier other than backerboard ? Like thick mil plastic? If so, how thick and on top of which substrate should the plastic be applied?
3) Can backerboard be adhered directly to an old plaster wall? If so what is the best way?
4)Do you recommend metal or wood studs for framing out the wall/shelves on the short sides of the tub?
Hi Eli,
1. I prefer to strip it down as far as I can and build up from there, but you can go over the linoleum as long as it’s bonded REALLY well.
2.No, no reason to.
3. It can with tapcons, but it’s a very iffy process and I don’t trust it.
4. I prefer wood, but metal works just as well (normally).
Thanks so much Roger!
Hi Roger,
I did a full bathroom renovation about 3 months ago, and noticed a crack in my grout going the width of the bathroom on only one grout line today. I am very certain that my substrate was well prepared, but clearly the tiles are moving on that part of the floor.
Can I simply take up the tiles on either side of the one grout line, and “reinforce” the floor along that area using more of the appropriate screws for HardieBacker board? I have not noticed any cracking along any other area of the floor.
Anything you could offer for advice would be great. I hope to avoid installing the entire floor again.
Best.
Tim
As a side note, I just noticed that I posted this on the wrong area of your site. After reading about cracked grout lines, I navigated here to make sure that I installed my substrate properly. I hope this is not a problem.
Best.
Tim
No problem at all Tim, I get all of them in the same place in the back room.
Hey Tim,
You can do that if you want, but simply putting more screws won’t fix it. You can, however, remove those tiles and tape and mud the seam with thinset and alkali-resistant mesh tape. That’s likely what’s causing your cracking (lack of it).
Roger,
I think I have read everything on your site by now. Great stuff. Nice to find someone that knows more than me and can give a correct answer.
I have two questions.
I put down cement board in my mudroom, approx. 8×16. I mixed in some old boards circa 1986 with the newer “lite” boards. I used the cement board screws. I had no trouble with the new boards but the heads don’t set fully in the old boards. We used to use roofing nails with the boards over thinset in my early days. The heads are mostly about 1/32 high, with a few maybe 1/16. I am going with 12×12 porcelain tile. The board is already down tight and the thinset set.
Can I tile over this without an issue?
Should I remove them and nail?
Or should I battle them in by pulling them out and rescrewing in the same hole?
By the way, I considered the above one question. That leave me another!
Is there more than one satisfactory way to tape the seams? I seem to recall you mudding the joint then embedding the tape. The joints are about an eight. In the past we used to apply the tape and then mud over, same as you would do a drywall joint. Is it necessary to fill the crack completely? If so, can I fill the crack and trowel clean, let dry, tape and then cover? I have always had trouble setting tape in spackle or mud without it looking like a two year old did it.
Thanks for your expert advise.
Al
Hey Al,
The amount of thinset under your tile should be more than enough to compensate for those. It shouldn’t be an issue. If you want to remove them and redrive them, they may sit flush, but they may just strip and cause more problems. I’d just leave them. Just fyi – roofing nails are still approved, and can be used, for cement backerboards.
You can tape the seams in any manner you wish. The purpose is to force both boards to move in the same direction when, and if, one of them does. As long as you have tape and mud over the top of that seam it will prevent differential movement. That’s the goal.
Roger,
Thanks for the timely advise. I didn’t think you would respond in time what with it being a holiday weekend and all.
I reset the worst screws and will hope for the best on the others. I also decided to mud the joints before taping. I have done a lot of tear outs in the past and not much gets through the tape.
New questions if you don’t mind.
In the old days, we used to snap a line and then spray paint it so it didn’t get wiped off when laying VCT. Worked great. I was thinking of doing the same thing for the tile but not sure if it will show thru the thinset. What is your recommendation for getting a nice straight line. The room I am doing is about 8×16. I was thinking of doing a 4×16 run to one wall and then following with the other side. Do you recommend nailing in a straight line? Interested in your experience because this is probably going to be very visible.
I am thinking of using a matching base molding around the room later after the walls are repainted. Sheetrock with minimal chance of getting wet. Can I just use a mastic for this?
I was thinking of using cardboard strips under the base to give me a uniform gap to caulk. Any better way to do this?
Last an probably most important, my fiancé wants these 2×2 accents in the center., I have never done these. It means I have to cut the porcelain tile to fit them in. I bought a carbide tile to chamfer the cut edge. Any advise if this is the correct way and tool? Do I just break the sharp edge?
These accents are the same thickness as the tile. Should I put them in as I lay the tile? I noticed in one of your other articles that in some cases you put them in after.
You are doing a great service. There is so much wrong advice out there. I don’t know how these people stay in business!
Sorry for the length. I type faster than I think.
Al
PS.
I mentioned I had trouble with the old board getting these screws to set. I tried three different type drills. Anyway, the new boards were the Wonderboard Lite. My sheetrock screw gun worked fantastic with these. Fast and uniform set flush or just below the surface. If you haven’t tried one, I recommend it for the Lite boards at least. Not sure how it would work for other boards.
Al
Thanks Al. It may help someone here. I actually use a Senco – a power driven collated screw gun. I’m lazy like that.
Hey Al,
You can still use chalk lines, I do too. Just comb thinset right up to the line and lay your tile. It will not show through the thinset. Yes, you can use mastic for that.
Tile wedges are a better option, although the cardboard works. It’s just difficult to get it out sometimes.
For the cut edges for the inserts just get a rubbing stone, it looks like a stone to sharpen knives. It will smooth out those cut edges. You can install them at the same time if you want. Normally I only install them afterwards when they are a different thickness. It ensures they get set flush and stay in place.
Wasn’t sure if I should move to a different section. Almost ready to start setting tile. Fear rules though. I am using 3/8 thick porcelain tile. In my trowel collection I have 1/2×1/2 notch and 1/4×1/4 notch. I have seen 5 different answers to what is the right size. I figure the 1/2 by 1/2 is appropriate but maybe overkill. I think if I was to pick one up right now I would probably go for a 1/4×3/8 deep notch. What would you recommend? Am I okay with the half by half or should I pick up something different. I don’t want to find out after the tile is covered in mud I should have went with something else. I figure the height of the notch is really what matters since it sets how thick the mud is under the tile. At a 45 degree angle a half inch notch should leave about 3/16 inch. Seems a bit much. A 3/8 notch would leave about and eight which seems like enough. Thanks for your help again. I am really overthinking this. This is why I had to quit contracting and go back to engineering. Paralyzed worrying about things most people will never even notice!
Hi Al,
Doesn’t matter where you put it, I get them all. I would pick up a 3/8 deep by either 3/8 or 1/4 trowel. It will, contrary to what engineers think (sorry, had to – I used to be a physicist…) not leave half the amount of thinset on the floor at a 45 degree angle. They trowels are made to use at a 45 – they leave that much on the floor when used at an angle. As long as you have full coverage beneath your tile, without excess squeeze-through, it’ll be fine. If you set the tile with this method you’ll have zero squeeze-through.
I’m a contractor and I’m going to put deco-poz microtopping by Ecoprocote over hardie board for a restaraunt job. Any advice would be appreciated. I have done a floor with 1/4 plywood underlayment, but had micro cracking so am switching to this backerboard. I can send pics if you wish.
Hi Hubris,
It’s a good product for certain applications, and the hardi is one of the substrates which will work well for it. You did not say, however, whether it is going on a floor or wall. If on a floor you need to also be concerned with the deflection of the framing. I don’t know what the acceptable deflection criteria are for deco-poz, but I would check on that before doing a floor over framing with it. The hardi will add no structural support to make up for lacking deflection. If you’re going over a wall it should work quite well.
Hello Roger,
Thanks for all the great info on your site! I am in the midst of renovating the only full bath in my house — we have an older house (1918) with T&G subfloor and what I assumed was a layer of hardwood and several layers of linoleum/vinyl tile & topped off with this awful rubbery sheet flooring.
I was planning to pull up everything down to the T&G and then lay down plywood & durock but when I pulled up the sheet flooring it appears that there is a solid ~1″ of concrete?! It is relatively smooth, although there are some uneven parts (i’d say between 1/8″-1/4″) — my questions are can I tile right on top of this and address the uneven parts with thinset or do I need to us a SLC first? Or – is it not suitable for tiling on top of at all & I have to try to get out all that concrete?
oh, and if it matters, we are installing basket weave mosaic tile on the floor
Hi Sarah,
You can tile right over it. That’s likely what was originally there. SLC would be a good choice, but you can use a medium-bed mortar to set your tile and you can fill them in as you tile (it won’t shrink as much as regular thinset).
Hi Roger, how’s it going? Well so far so good, I cut the old fiberglass tub out, removed the sheet rock from the walls and ceiling and vacuumed out everything. What a messy job. The floor was 5/8 and I’m going to replace it with 3/4, but first I have a lot of blocking to do. I want to use 1/2 hardi on the walls and 1/4 on the floor with Ditra over that. I,m not to concerned with the additional height I figure that I can make it up with the threshold. My questions are should I run the Ditra under the threshold also, use the same thin set to attach the Hardi to the plywood and the Ditra to the Hardi, which is spec’d for unmodified, and do I put silicone in the gap between the different plains? Thanks man, sorry if my question is a little disjointed I’ve got a million things running through my gourd about this bathroom. So long for now, Mike.
Hey Mike,
There is actually no need to use hardi on the floor, the ditra can go right over it with modified thinset. Hardi adds nothing structurally so all your gaining is height – literally. If you are using a tile or stone threshold then yes, put ditra beneath it too. If you’re using wood then no. If using schluter or another transition that goes under the tile side then yes, ditra under it as well.
Roger,
I am installing a american std tub 60″ by 30″ and will be tiling the floor and surrounds. the tubs mft says to butt the substrate against the apron of the tub. you’re saying leave 1/16″ inch around the hardieboard. please advise. how have you handled this in the past. fyi it is a small guest bathroom 5 ft wide. I had planned to not stagger but install the hardieboard by width. also, should i still cut and stagger in small rm? thanks
Hi Joseph,
Yes, you need room for the different materials to expand and contract without stressing against each other. So you should leave the 1/16″ gap. Any backer used for a flooring substrate should be staggered, no matter the size.
Roger,
I tried taking your advice and put down some mesh on my Hardiebacker seam. I missed the detail that said you do it as you lay tile. Now it is hard and causing an uneven seam. Should I scrape it out or can the tile thinset can adsorb the unevenness? With a 24″ long tile straddling the seam either end can rock up or down a good 1/8″.
Details: 4’x6′ bathroom floor, 24″x12″ porcelain tile. (not installed yet)
Substrate top down:
–3 coats Redgard
–1/4″ hardie board
–thinset
–1/2″ ply
–solidwood subfloor
Thanks
First-timer.
Hey Joe,
Yes, you can make up for that (1/8″ rock means it’s likely less than 1/16″ higher than the backer) with the thinset if you want. You can also just sand down the seams with sandpaper or a brick.
Yes, a brick, it’ll sand thinset.
What if the surface you start with is concrete?
Than you don’t use cement backerboard. It is only for use over wooden substrates.
¡Hola Roger! :O)
We would like to embed WarmWire into mostly likely a SLC bed.
This weekend, we are installing Hardiebacker over Modified Thinset (Laticrete’s 253).
After the Hardiebacker has been screwed into the subfloor, what type of thinset (modified or unmodified) do you recommend for embedding the alkali-resistant mesh tape in the seams between Hardie sheets?
Thank you,
Holly
Kansas City
Hi Holly,
Same thinset you used beneath it is just fine.
Wow! My grouts cracking and coming out! I did the Prep work and I thought I did real good job. I hired someone to tile for me. I strengthened the floor under the house and then put hardy board down with thin set and screws every 6 inches. It seems like I did real good job reading your write up. The floor tiles are 12 inches by 3/8 of an inch thick and it seemed like an easy job but my dogs on fire. The grouts coming out. The guy doing my tile work was slow. I know that he added water to the grout at least once while he was grouting. Also while he was laying the tiles he lost one tile and had to re-cut it while the thin set was probably hardening up. What do you think?
I don’t want my dog to burn to death!!!
It sounds like there may be either not enough coverage of thinset beneath the tile or there is a problem with the grout itself (unlikely, but possible). Do any of the tiles around the cracking sound hollow at all? If so it was not installed with proper coverage or the thinset was skimming over when the tile was placed into it.
Good evening,
I need help!!!
I put backerboard over plywood in a thinsetbed in a very small bathroom,
60″ x 60″ backerboard in 2 pieces. After connecting the first piece with the srews ,one side of the backerboard pops up in an aerea 24″ x 24″ 3/8″. It`s not connected with the thinset and plywood.
Maybe one of my mistakes is that I put the backerboard in the thinsetbed one day and srewed the next day.
what can I do???
how can I cut it out?
Thank you for any idea!!!!!!!!
Hi Gunda,
Is it popping up because the floor is uneven? I assume so. Part of the reason it that you waited, the other is that even had you not waited there is apparently not enough thinset in one of the areas to allow the backer to lie flat and have it fully supported. Unless it’s not due to an uneven substrate. If you remove the screws you’ve installed and screw down the area that pops up first will it lie flat? Or is this area not connected to begin with (before you install screws)? If that’s the case you need more thinset beneath that area.
Ideally you should remove the backer, put down a fresh layer of thinset. Then screw down the backer while the thinset is still wet. I honestly don’t know how to tell you to ‘cut it out’ if I don’t know why it’s doing that nor how well it’s bonded to the floor with the thinset. I need to know why it’s doing what it’s doing before I can tell you how to fix it.
I plan on tiling a small bathroom. It’s 6′ long 4′ wide and 8′ tall. No tub, just a sink and toilet. I plan on tiling the floor and the walls all the way to the ceiling. Should I install the Hardie Backer boards on the floor or the walls first? The same question for the tiles. Do I tile the walls or the floor first?
Hey Tom,
Doesn’t really make any difference. I prefer the floors first, both substrate and tile.
Roger, excellent website and great humor …or maybe you are serious and that would explain the flaming dogs I passed by the other day.
I am preparing to tile a small 4.5′ x 4.5′ powder room, decided to do some online sleuthing for tips and such, found your website, bookmarked, and have probably read half your posts by this point. Thanks to all your explanations I am pretty well set now regarding proper installation for all the layers that are *below* the actual tiles. I did notice you mention “deflection stability” and “minimum subfloor thickness” and (being a DIY-hypochondriac) am now concerned that my particular project may not be stable enough leading to cracked grout, broken tiles, caved-in-roof, and Scurvy. As funny as it was to read through your long page titled “Flawed”, I’d rather not be inducted into that particular archive.
So what I have is your standard 70’s cookie-cutter pile-o-crap house. The powder room floor joists are 2×8 at 16″ on center. The subfloor appears to be 3/4″ plywood (although I might be wrong and have 1/2″ plywood instead – they were pretty cheap in the 70’s). My plan is to put thinset on top the 3/4″ (or 1/2″) plywood subfloor, 1/2″ cement backer (brand name: Wonderboard), thinset the joints, tape the joints, thinset on top to set the 12″x12″ tiles.
So my questions are:
1) Will the 3/4″ plywood subfloor with the joists 2×8 @ 16o.c. be enough support under the 1/2″ cement backer to keep grout & tiles from cracking due to deflection?
2) Do you thinset inside the joint between backer pieces (under the tape), or do you just leave air in the joint between backer pieces?
3) The entrance to the room is tongue-n-groove hardwood flooring. Can I tile to within 1/4″ of the hardwood T&G floor and use a matching color tile caulk to fill the gap, or is that asking for more flaming animals?
Also, do you have any books for sale? If this small project goes well I will need a good resource when we finally tear out our crappy kitchen and I have a larger tiling job on my hands.
Hey Jim,
1. Maybe, maybe not. The unsupported span on the joists need to be taken into consideration as well. this is the distance between the vertical supports of your joists. If they are 10 feet apart that translates into a deflection ratio of L/480, which is the minimum for ceramic or porcelain tile. The shorter the distance of the span the better – more support. Ideally, and by standards, you should also have an additional layer of plywood over that. I would put another layer of 1/2″ over it. If you’re concerned about height you can use 1/4″ backer over it, thickness of the backer makes no difference in your flooring deflection, only that you have thinset beneath it.
2. Yes, fill the gap, put your tape on it and skim coat. Like taping and mudding drywall.
3. Yes, but I usually go to 1/8″ from the hardwood and use silicone.
My Library tab has all kinds of manuals for tile installation having to do with showers (and a basic layout and design manual). These are pdf’s (ebook) and you may feel free to spend your extra beer money on them.
Yeah, I just measured and the joist span is 10′ between my outside cinderblock wall and the central I-beam). Wow, my house is only 20′ deep…. that sucks.
I had already bought and dry-laid the 1/2″ backer, but it’s just a 4×4 room so I will go pickup some 1/4″ backer and some 1/2″ plywood like you suggest and do this right. The only downside will be the 1/4″ height difference between the tile and the T&G floor, but I’m sure the Big Box stores sell a thin reducer strip. I have kids that leap over entire sofas in a single bound so I am confident they can handle a 1/4″ reducer as they tear into the bathroom to use the toilet.
Thanks for the advice!
Question about answer to #2.
I though that the space between the board was needed in case of movement. Doesn’t adding thinset in the crack and taping and thinset(ing) over go against that?
*love the site, although I feel like
sometimes with my kitchen reno.
thanks
The space around the perimeter is for movement. The space between the boards is to be able to tie all the boards together to create a monolithic structure.
Roger,
Thanks for the website and all of your helpful information. I am almost done with my bathroom project and have a question regarding Hardibacker cement board. I have more than several scrap pieces of Hardibacker lying around from previous projects. Can I use those pieces on my bathroom floor as long as I stager the joints, thinset underneath each piece and tape? Would too many separate pieces of Hardibacker create a problem with my floor tile? Flexing, stretching, cracking, movement?
Hey Erik,
As long as you’re talking about 2 or 3 foot scraps and not four inch scraps it’ll be fine as long as you tape and mud them with alkali-resistant mesh tape and thinset.
Thanks Bro……
Roger, yes 1/4″ plywood then, and vinyl tile, Great Idea!!!! Thanks a Million, and Wow!, great site, you answered my question within one day. Greg
I am installing radiant heat under new tile in a bathoom with a walk in shower using a trough drain. I need the floor at the shower entry to be 7/8″ higher than at the back of the shower. The radiant heat area will have thinset, cerazorb underlayment and SLC amounting to 9/16″. That means I need to either add another 5/16″ to that area or lower the shower pan base by 5/16″. It would seem adding 1/4″ hardiboard to the floor with 1/16″ thinset would be easier than notching the joists 5/16″ and bracing them (to what degree?) or introducing a double joist in the floor joist and boxing the pan 5/16″ lower (which I can’t do without blocking a heating duct below the floor). Ideas? Best options?
Hey Todd,
First of all you’re working all your numbers with exact measurements – you don’t want to do that. That said, the difference between 5/16″ and 1/2″ is 3/16″. When dealing with building up heights of flooring substrates that number is negligible. What I would do is put a 1/2″ layer of plywood or backer beneath your radiant heat.
Easier than that, though, would simply be to add SLC up to the level you need above and beyond what you’re already doing.
Not sure where you got the “difference between 5/16″ and 1/2″ is 3/16”. My calculation was 7/8″=14/16 less the 9/16 = 5/16 (not 3/16″). But I guess I don’t understand your point about not wanting to work with exact numbers. What then? Also, adding 1/2″ plywood makes the floor 1/4″ higher (at the threshold to the room necessary. So why not 1/4″ board? Seems easier than mixing another batch or two of SLC.
Then do it that way.
I did reword that incorrectly, it was clear in my mind.
Your total height at the shower entry that you wanted was 7/8″. The difference between that and 1/2″ plywood, and that and the 5/16″ you stated you needed, is 3/16″.
With ANY substrate or tile product you install you should not work height differences with exact numbers. The amount of thinset, inconsistencies in the substrates, inconsistencies in the tile, etc. will nearly ALWAYS throw your exact measurements off. If you work with precise numbers like that and one of those things throws it off by even 1/16″ or 1/8″ you’re screwed somewhere.
Your tile installation and substrate should not depend on a height difference at the adjoining flooring less than 1/2″. Why not 1/4″ board? Because you want to work with exact numbers and that leaves your threshold 1/16″ higher. 1/4″ ply has about 75% less structural stability as does 1/2″. When you are working with tile and stone installation, especially with radiant heat where there will be extreme amounts of expansion and contraction, you want as much structural stability as you’re able to provide.
The difference, by the way, between the 1/4″ higher threshold you’ve pointed out and the 1/16″ difference above – is 3/16″. If you need to provide a threshold to compensate for height differences an additional 3/16″ for 75% more substrate strength is worth it every time. If you want it even use the slc.
Mixing another batch or two of slc takes, at most, an hour with mixing and installation. Given that the average replacement window of a tile installation is around 15 years I think that an extremely small price to pay for a level transition if that’s what you want.
Are you an engineer or an accountant?
(That, by the way, is not an insult or jab at all, a lot of people take that the wrong way.) I was a physicist, so if you’re an engineer you’ll fully understand that question. 